In a patient image where a patient (test object) is taken, a coordinate system (also referred to as clinical angle coordinates) using a clinical angle as a coordinate system indicating the imaging direction is generally used.
The coordinate position indicated in the clinical angle coordinate system is determined on a side of a holding device, which includes an X-ray tube and an X-ray detector, as a positioning result by a drive shaft (movable shaft) of the holding device.
That is, a typical X-ray image diagnostic apparatus assumes a state where a bed position (top table position) is fixed. The apparatus determines a coordinate position in the clinical angle coordinate system according to the positioning result between the X-ray tube and the X-ray detector on the baths of drive control for the drive shaft (movable shaft) controlled on the side of the holding device.
Such a typical X-ray image diagnostic apparatus positions the apparatus only on the basis of drive control on the side of the holding device, and calculates the clinical angle coordinates as an angle for taking an image of a patient (test object) according to the positional relationship with the bed position (top table position) in a fixed state.
As described above, the clinical angle coordinates is thus calculated only on the basis of drive control for the drive shaft (movable shaft) of the holding device, which includes the X-ray tube and the X-ray detector. Conventionally, the bed position and the top table position, which include the patient to be imaged, are not considered at all.
Accordingly, the turning angle of the top table provided for the bed and the tilt angle of the top table are not reflected at all in the clinical angle coordinates calculated by the holding device. For instance, when a turning shaft (drive shaft) of the bed is driven to change the top table position and in turn change the turning angle of the top table and the tilt angle of the top table, the clinical angle coordinates calculated on the side of the holding device sometimes indicate an incorrect coordinate position.
To address this problem, an X-ray image diagnostic apparatus capable of calculating clinical angle coordinates that always indicate correct position and angle has been desired.